Fluoride alters connexin expression in rat incisor pulp

Objective: Connexins (Cxs) are important to control growth and cell differentiation of dental tissues. The aim of the present study was to assess the impact of chronic exposure to sodium fluoride (NaF) on Cxs expression and alkaline phosphatase (ALP) activity in dental pulp, and on morphometric parameters of adult rat mandible and incisors. Design: Three groups of male Wistar rats (22 days-old) were given water containing: (a) 0.3 mg/L (Control), (b) 10 mg/L and (c) 50 mg/L of NaF for eight weeks. Incisor pulp homogenates were prepared for determination of Cx32, Cx43 and Cx45 gene expression, using semi-quantitative RT-PCR, and of ALP activity. Morphometric parameters of mandible and incisors were determined on radiographs. Results: Cx43 gene expression increased with exposure to NaF in a dose-dependent manner. Cx32 mRNA levels were higher than controls in the 10 mg/L NaF group only; Cx45 mRNA levels were lower in groups given 10 and 50 mg/L of NaF than in controls. ALP activity was higher in both high-NaF dose groups compared to the control group (p < 0.05). Lower incisor diameter was lower in the 50 mg/L NaF than in the control group (p <0.01). None of the mandibular growth parameters were affected by NaF treatment. Conclusion: Our results showed that fluorotic alterations in rat incisor were associated with increased Cx43 expression and ALP activity, as well as with changes in the expression pattern of different Cxs in pulp tissue. The observed changes may have a stimulating effect on dentin mineralization. (C) 2014 Elsevier Ltd. All rights reserved.